Unraveling the Knowledge Roadmap of Building Policy Mixes: A Scientometric Analysis

Abstract

Improving energy efficiency and reducing carbon emissions from buildings are crucial for achieving sustainable development. To realize these goals, it is essential to adopt a policy mix. However, despite much effort in this field, there is a lack of comprehensive understanding on building policy mixes (BPMs), which challenges building sustainability. To address this research gap, this study attempted to uncover the knowledge landscape of BPM through scientometric analysis. By employing methods such as keywords co-occurrence analysis, clustering analysis, co-citation analysis, and research trend analysis, this study systematically examined the current status, hot topics, underlying knowledge framework, knowledge domains, and frontiers of BPM research. The findings revealed that the existing BPM research primarily focuses on various aspects, including policy-related topics such as building energy efficiency policies and policy instruments, as well as topics like green affordable housing, hindering factors, carbon pricing, use obligation, construction waste reduction, and sustainable construction methods. Furthermore, the analysis identified research frontiers in BPM, encompassing policy considerations (e.g., building efficiency policy, split incentive, carbon tax, and carbon pricing), energy-related aspects (e.g., consumption, green transition), political dimensions (e.g., governance, management), building-related factors (e.g., green building, retrofitting), the innovation system, and the evolutionary game. Based on these findings, this study suggests that future research in BPM can deepen insight into interdisciplinary policy mixes by focusing on policy strategies, processes, and features. This study contributes to a holistic understanding of BPM and offers insightful guidance for both researchers and practitioners seeking to advance sustainable practices in the building sector.

1. Introduction

Decarbonization and improving energy efficiency are crucial strategies to address a range of climate- and resource-related challenges, including climate change and resource scarcity [1,2]. They represent key initiatives in the pursuit of sustainable development [3]. A significant focus of these strategies lies in the building sector due to its substantial energy consumption and greenhouse gas emissions. The sector’s energy consumption is particularly evident during the phases of construction, use, and demolition, accounting for 40% of the world’s overall energy usage [4]. Additionally, it directly or indirectly contributes to approximately one-third of the world’s CO₂ emissions associated with energy production and related processes [5].

Extensive efforts have been devoted to reducing carbon emissions and improving energy efficiency in the building sector. Examples of these include developing green buildings [6], zero-energy buildings [7], building retrofitting [8], low-energy architecture [9], and green material and techniques [10]. Additionally, various policy regulations and initiatives have been introduced across the world [11,12,13], which are crucial drivers of building sustainable development [14,15].

Nevertheless, there are many challenges with these academic and practical explorations, such as the effectiveness of policies [16]. The building sector involves multiple stages such as investment, design, material supply, construction, and operation. It is a complex system with numerous stakeholders and significant societal and environmental impacts. The inherent characteristics of the building sector make it challenging for a single policy to effectively drive the decarbonization of this system and improve its energy efficiency. As a result, researchers have looked into using a policy mix. A policy mix refers to a diversity of policy instruments embedded in and following different policy rationales and goals [17], which can help overcome systematic challenges [15]. Furthermore, Ringeling [18] highlighted that a policy mix goes beyond being a simple combination of policy instruments; it encompasses the dynamic process through which these policy instruments interact and influence each other. Schwarz et al. [19] analyzed how a combination of different policies can be effective in closing the energy efficiency gap. They detected that the type and timing of policy mixes are the key. Braungardt et al. [20] explored the consistency of the decarbonization policy mix by employing carbon pricing strategies and highlighted the importance of policy complementarity. In spite of much exploration into policy mixes, Rogge et al. [21] argued that existing studies often fail to reflect the complexity and dynamics of actual policy mixes. Moreover, the complex features of the building sector necessitate comprehensive and tailored policy mixes. Effectively addressing this complexity remains a significant challenge, thus highlighting the need for a deeper understanding of policy mixes specifically within the building sector.

The aim of this study is to provide a comprehensive understanding of BPM by thoroughly reviewing the policy mixes in the building sector. To this end, this study includes: (1) a collection of the related literature, (2) a scientometric analysis of the literature to examine the current state of research, hotspots, domains, and trends, (3) developing a BPM knowledge roadmap and identing research prospects, and (4) the conclusion to this research.

2. Materials and Methods

2.1. Research Methods

The primary objective of this study was to map BPM knowledge by investigating its research status, hot topics, underlying knowledge framework, knowledge domains, and frontiers. This endeavor aimed to establish a solid foundation for a comprehensive understanding of BPM research. In spite of potential bias, previous studies [22,23] have indicated that the discipline of scientometrics, compared to qualitative literature research methods, is an objective and valuable tool that can be employed to achieve these research goals. Scientometrics, as a scholarly discipline, encompasses the visualization and mapping of knowledge domains [24]. Its primary functions include providing a descriptive account of the process of scientific development, elucidating the inherent mechanisms driving scientific progress, forecasting future trends in scientific advancements, and establishing a solid foundation for scientific management endeavors [25]. Being an applied discipline, scientometrics relies heavily on quantitative analysis methods to investigate subjects and entities that reflect scientific activity. It employs academic datasets to effectively map and analyze the structure and evolutionary patterns of these domains [26].

A variety of scientometric tools have been employed in diverse research domains, such as Cite Space [27], Vos-viewer [28], and Gephi [29]. Each analytical tool offers unique functions and advantages. Cite Space, in particular, distinguishes itself with its powerful visualization capabilities and dynamic adjustment features [30]. For instance, He et al. [31] utilized Cite Space for visual analysis and introduced a knowledge graph for building retrofitting. Li et al. [32] employed Cite Space to map a knowledge graph regarding research on stakeholders in green buildings. Xu et al. [33] explored the evolutionary path and developed a knowledge roadmap regarding residents’ energy consumption behaviors by using the Cite Space tool. Consequently, Cite Space 5.7 R5 was selected as the tool for analyzing the literature relevant to BPM in this study.

2.2. Data Collection

The retrieval of scientific sources based on key terms can be accomplished using various online tools, such as Scopus and Web of Science [34]. Scopus offers a broader coverage of journals and includes more contemporary resources [35]. Web of Science (WOS) is widely regarded as a vital resource for bibliometric analyses due to its extensive information and the high quality of its indexed journals [36]. Consequently, these two databases were chosen as the source databases for this study.

A systematic literature search was conducted using synonym substitution to gather relevant publications in the field of BPM. Initially, a total of 620 publications were collected, consisting of 218 from the Scopus database and 402 from the WOS database. Subsequently, the collected articles were imported into Endnote X9 and underwent a deduplication process, resulting in a final set of 531 unique articles. These 531 articles underwent further screening based on their titles, keywords, and abstracts. For articles with uncertain relevance, a comprehensive full-text reading was conducted for screening purposes. The screening criteria primarily focused on the relevance of research topics, encompassing both building and policy mixes. Ultimately, we identified 67 articles that met the criteria and were deemed relevant, which were then selected as the sample literature for our study. The detailed process of the data collection is illustrated in Figure 1, while the specific search criteria and guidelines can be found in

Table 1. Data search criteria and guidelines.

Steps	Data Search Criteria and Guidelines
Inclusion criteria	Only academic research on BPM published in English could be included in this study.
	This study aimed to comprehensively search for relevant studies without limitations on the time or country of publication.
	The data for this study were exclusively sourced from two databases, namely Scopus and WOS.
Exclusion criteria	This study specifically concentrated on policy mixes within the building sector, thereby excluding studies on policy portfolios outside of the building sector or within the building sector that were not directly related to policy mixes.
	Excluding newspapers, announcements and science propaganda materials, among others.
Data search strategy	For the search process, synonym substitution was employed using the following search terms: “polic* mix*” “instrument* mix*”, “polic* portfolio*”, “polic* package*”, “polic* interplay”, “polic* interaction*”, “polic* combination*”, “polic* synerg*”, “polic* integrat*”, “building*”, and “construction*”.
Retrieval time	18 May 2023

.

3. Results and Discussion

3.1. Sample Distributions

The temporal distribution of the 67 literature items is depicted in Figure 2. It can be observed that the initial investigations on policy mixes within the building field emerged in 2004, which was followed by a steady but limited number of relevant studies in almost every subsequent year until 2014, with the exception of 2005. Starting from 2015, there has been a notable increase in the number of related studies, culminating in a peak in 2019 with 11 articles. This temporal distribution reveals the developmental trajectory of research in this field, indicating growing interest and attention from researchers. The peak in 2019 suggests a heightened focus on policy mixes within the building sector, reflecting the significance and popularity of this research topic during that period.

It is worth noting that in 2023, there were only six publications pertaining to this research domain. However, this does not necessarily indicate a decline in the significance of the related research. Instead, it can be attributed to the fact that the literature collection was concluded in May 2023. Therefore, it is possible that additional research is currently underway or remains unpublished. This further underscores the ongoing vibrancy and future potential of research in the field of policy mixes within the building sector.

Figure 3 illustrates the geographic distribution of the relevant studies, primarily concentrated in 27 countries and regions. Notably, China leads with 10 studies, followed by the Netherlands (7), the United Kingdom (6), Germany (6), Austria (6), and Australia (5), collectively accounting for over 60% of the total literature. These countries emerge as the primary contributors, indicating a significant level of research activity within this field. Additionally, the remaining studies exhibit a dispersed distribution across various countries and regions, including Sweden and Greece, with the number of relevant studies ranging from a maximum of three to a minimum of one. Despite their relatively smaller numbers, these countries and regions still make valuable contributions to the overall body of research.

3.2. Keywords Co-Occurrence Analysis

Keywords play a crucial role in summarizing and condensing the content of a research paper. Analyzing keywords enables a quick grasp of the research hotspots within a specific field. Keyword co-occurrences, which refer to the appearance of keywords together in at least two distinct articles over a period, provide valuable insights into the interrelationships among keywords [37].

Utilizing Cite Space, we conducted a comprehensive visual analysis of the titles, keywords, and noun phrases in the abstracts of the literature. By integrating synonymous keywords, we constructed a keywords co-occurrence network that comprised 117 nodes and 273 interconnected lines, as illustrated in Figure 4. Within this network, the size of each node signifies its relative importance or contribution to the overall literature network. Larger nodes indicate a higher level of significance within the literature network [38]. The connections between nodes represent the co-occurrence of keywords within the same literature, highlighting their interrelationships. Additionally, the color of the connecting lines conveys the temporal dimension, indicating the chronological order of keyword appearances [39].

As depicted in Figure 4, the larger nodes include building energy efficiency (13), building (11), policy mix (9), barrier (5), climate change (4), China (3), governance (3), energy efficiency policy (3), discount rate (3), and performance (3). These nodes reflect the significance of these topics and represent the research hotspots [38]. The blue lines in the figure represent early-stage research, whereas the red lines indicate recent research. It is evident that these larger nodes often serve as connections between different-colored lines, indicating that these nodes have been studied in various periods. From the perspective of different-colored networks, it is apparent that the red network section is larger and covers a wider range of keyword types, while the blue network section has fewer and thicker connections. These results indicate that early-stage research covers fewer topics and demonstrates close interconnections between them, whereas recent research encompasses a broader range of research focus.

Considering the complexity of the keywords in Figure 4, they are primarily divided into six groups (as shown in

Table 2. Keywords groups.

Group	Keywords	Frequency	Group	Keywords	Frequency
Policy	Policy mix	9	Politics	Governance	5
	Climate policy	3		Management	3
	Energy efficiency policy	3		Impact	3
	Environmental policy	2		Performance	3
	Policy package	2		Politics	2
	Split incentive	2	Energy	Building energy efficiency	13
Region	China	3		Energy	2
	Australia	2		Energy transition	2
	The UK	2		Renewable energy	2
Building	Building	11	Innovation	Innovation	3
	Green building	3		Innovation system	2

) by integrating semantic meanings of keywords, aiming to establish an initial and comprehensive understanding of the research landscape. These groups encompass policy, politics, region, building, energy, and innovation. Taking policy and politics as an example, specific aspects of policy include environmental or climate policies, policy mixes, and incentives. Regarding politics, the primary focus lies in policy formulation and its effectiveness, encompassing governance, impact, and performance.

3.3. Keywords Clustering Analysis

Keywords clustering analysis aims to identify research domains [30] by uncovering the underlying structure of keywords [40]. This identification of the inherent structure is accomplished through the utilization of specific algorithms embedded within Cite Space. Drawing upon previous research [41], the log–likelihood ratio algorithm was employed in this study to facilitate the identification of label words for keywords clustering. Additionally, the effectiveness of keywords clustering can be evaluated using the Q-value and S-value [42]. A higher Q-value indicates a stronger association between keywords and a better clustering effect for a particular number of clusters. The S-value represents the average silhouette score of the clustering algorithm, with higher values indicating more effective and reliable clustering outcomes. However, an S-value approaching infinity suggests the presence of only one cluster, indicating a potentially limited network representing a single research topic exclusively. Generally, a Q-value greater than 0.3 signifies a significant clustering structure, while an S value greater than 0.5 indicates reasonable clustering [43].

To enhance our understanding of the research conducted in this field, a keywords clustering map (Figure 5) was developed. The clustering map exhibits nine discernible clusters. The Q-value for Figure 5 was calculated as 0.7873, while the S-value was determined to be 0.9327. These metrics indicate that the clustering map is significantly effective, offering a comprehensive overview of the field. It is worth noting that the cluster size is inversely proportional to the cluster number, meaning that larger numbers correspond to smaller cluster sizes [44]. The largest cluster is labeled as #0, while the smallest cluster is labeled as #9.

Cluster #0, labelled as “environmental policies”, contains keywords related to “performance”, “evolutionary games”, “simulation”, “green housing”, “building policy”, and “innovation”. This research section evaluates policy instruments for improving building energy performance and simulates existing policies. For instance, a study conducted in South Korea quantified the specific emissions gaps between energy policies and climate policies by comparing different policy scenarios and combinations against committed climate policy targets [45]. Li and Shui [46] conducted a critical evaluation of building energy efficiency policies for existing and new buildings in China, and they discussed the public game dilemmas in green and sustainable building production within the context of China’s economic development and social transformation. Ziemele et al. [47] employed a system dynamic modeling approach to analyze the impact of economic mechanisms on carbon dioxide emissions from the heating systems in the Latvian region. The model incorporated three policy instruments, namely carbon taxation, solar technology subsidies, and energy efficiency renovation funds. Chen et al. [48] employed evolutionary game theory to develop a model and investigated the effects of four policy combinations on construction strategies. Their study analyzed the inherent mechanisms of behavioral evolution for both government agencies and construction enterprises, providing insights into the interactions and dynamics between the two entities in the context of policy implementation.

Cluster #1, labelled as “policy instrument”, encompasses keywords related to “consumption”, “energy”, “policy programs”, “building sector”, “urban planning”, “energy efficiency”, “complex policy issues”, and “top-down modeling”. This line of research primarily focuses on specific policy tools aimed at addressing policy implementation issues. For example, Sheng et al. [49] conducted a cross-regional analysis to elucidate how the effectiveness of energy-saving policies is influenced by climate conditions, specifically focusing on the actual performance of building envelopes. Fotiou et al. [50] compared different policy configurations, including economic measures (i.e., subsidies) and regulatory measures (i.e., energy performance standards). They found that the optimal policy mix is derived from a trade-off among various objectives, such as the cost-effectiveness of policy budgets and the distributional impact on different types of buildings and consumers. Gan et al. [51] indicated that a combination of three policy strategies—fiscal and price support, infrastructure development and technical support, and information guidance and certification labels—is the most effective approach for promoting the development of green housing in rural areas. Yang et al. [52] suggested that a combination of environmental taxes, green subsidies, and carbon trading would serve as a better policy tool for fostering the development of green building technologies.

Cluster #2, labeled as “green affordable housing”, includes keywords related to “demolition”, “incentive density”, “demand”, “determinants”, “building”, “regulation”, and “privatization”. This cluster of research delves into various aspects of green affordable housing, encompassing different stakeholders and policy considerations. For example, Jeddi Yeganeh et al. [53] investigated density incentive schemes for green affordable housing, exploring factors such as construction costs, transaction prices, green certifications, and the spillover effects of affordable housing units. Gram-Hanssen et al. [54] conducted exploratory research on local climate strategies and homeowner participation in energy retrofitting within prominent Danish cities. They found that national policy combinations only partially supported these local initiatives. Florencia Zabaloy et al. [55] highlighted that the implementation of residential energy efficiency policies is influenced by the national context, including commitment, awareness raising, financing access, and macroeconomic conditions. Webber et al. [56] conducted post hoc assessments of household energy use, providing insights into the energy consumption patterns of residents. Maerz, Bierwirth, and Schuele [12] emphasized the multifaceted nature of energy retrofitting decisions and the importance of comprehensive policy packages. They highlight the need to address specific investment behaviors of small-scale private homeowners and improve local framework conditions. Segal et al. [57] proposed an asymmetric decentralization approach that tailors policy options to local contexts, and they suggest using assessment outcomes to guide the allocation of nationally designated retrofitting funds.

Cluster #3, labeled as “hindering factor”, contains keywords related to “climate”, “impediments”, “design”, “benefits”, “policy mix”, “sector”, and “creative destruction”. This section can be further classified into three distinct categories, each addressing specific obstacles within the hindering factors theme. The first category examines hindrances associated with the policy formulation and implementation process, specifically arising from external environmental uncertainties. Chen et al. [58] emphasized that the turnover of politicians within regulatory governments is a noteworthy manifestation of such uncertainties, leading to policy discontinuity and changes in political relationships. Supporting this, Choi et al. [59] conducted a study in which 125 large-scale construction projects in Datong City, Shanxi Province, China, were temporarily suspended due to policy interruptions caused by political turnover. Furthermore, Xing et al. [60] suggested that uncertainty in environmental conditions can undermine the positive impact of regional policy combinations when it comes to implementing organizational building information modeling (BIM) practices. The second category focuses on barriers to consistency arising from differences in goals and governance approaches across various policy domains. For instance, excessive exploitation of building aggregates creates significant obstacles due to the prioritization of socioeconomic goals over environmental objectives [61]. Moreover, countries with highly federal and corporatist characteristics, such as Austria, often require additional political coordination in governance. Provincial actors tend to evade or delay national objectives unless pressured by European directives or national legislation [62]. The third category examines obstacles related to energy efficiency in buildings. Kangas et al. [63], adopting a supply-side perspective, qualitatively analyzed energy efficiency barriers in the Finnish building sector. They identify prominent obstacles, including a lack of technical skills, disinterest in improving energy efficiency, and ineffective regulations. Furthermore, different types of building owners face distinct barriers to energy-saving measures. Heikkilä and Kuivaniemi [64] found that office building owners often encounter long payback periods as the primary obstacle to improving energy efficiency. On the other hand, Miguel A. et al. [65] found that respondents with previous experience in non-energy-related home renovations, or with someone in the family network with experience in adopting energy efficiency measures are more likely to have investigated or completed an energy-related investment.

Cluster #4, labeled as “carbon pricing”, contains keywords related to “framework”, “dividend rewards”, “carbon prices”, “energy transformation”, “technology”, and “biological economy”. This type of research focuses on strategies related to carbon emissions in order to achieve a low-carbon energy transition. It is widely recognized that carbon pricing provides the most effective means of reducing carbon emissions and plays a crucial role in facilitating the transition to low-carbon energy systems [66]. Additionally, the findings of Braungardt et al. [20] highlighted the significance of complementary policies to achieve deep decarbonization in the building sector. In Luxembourg, it has been demonstrated that the implementation of a national carbon tax on existing buildings is essential for significantly improving the energy efficiency and adequacy of the sector [67]. Similarly, in China, a combination of environmental taxes, green subsidies, and carbon trading is proposed as a more effective policy approach for developing green industries [52]. Likewise, in Latvia, it is recommended to implement a policy mix that includes various policy instruments, such as a carbon tax, subsidies for solar technologies, and funding for energy-efficient renovation [47]. Furthermore, the development of the “bioeconomy” emphasizes the importance of biotechnology and bioresources for promoting green and low-carbon biomass substitution [68]. The study by Dietz et al. [69] suggested that greater intergovernmental cooperation and coordination at the international level are necessary to establish a framework for sustainable bioeconomy development.

Cluster #5, labelled “building energy efficiency policies”, contains keywords related to “policy implementation”, “policy tools”, “environmental rules and regulations”, “carbon emissions relief”, and “building energy efficiency”. These studies primarily focus on enhancing building energy efficiency, reducing energy costs, and addressing energy poverty, with a specific emphasis on the significant role of social housing and building renovation in building energy policies. The study of building energy policies can be categorized into several dimensions: technological advancements, social considerations, economic incentives, and knowledge dissemination. In the technological aspect, Li and Colombier [70] analyzed the current status and future prospects of building energy efficiency technologies in Chinese urban areas. They outlined the economic and institutional barriers that hindered the widespread adoption of sustainable, low-carbon, and net zero-carbon building technologies. Another contribution by Jones et al. [71] explored zero-carbon design and proposed an innovative approach to building envelope design. From a social perspective, building energy policies aim to not only address energy-related issues but to also consider the needs of residents. For instance, Chitnis et al. [72] estimated the income elasticity of 16 types of household commodities and the intensity of greenhouse gas emissions by considering the implicit emissions associated with energy efficiency measures themselves, as well as their capital costs. They noted that retrofitting residential buildings for energy-poor households may not always achieve the intended climate goals. However, it can improve the well-being of impoverished individuals and fulfill their essential requirements. In a similar vein, Kelemen et al. [73] developed a synthesis method for an online database on “energy efficiency research and innovation”. They stated that enhancing building energy efficiency brought multiple benefits to vulnerable groups, including reducing residential relocations, improving household comfort and safety, and decreasing carbon emissions. Regarding the economic aspect, Zhang et al. [74] conducted a comprehensive nationwide field survey to investigate the management of building energy efficiency in the Chinese building sector, specifically under energy performance contracting (EPC). They highlighted that relying solely on potential energy cost savings is often insufficient to incentivize investment in improvement measures, thus necessitating more effective approaches to induce or compel greater efforts. Bonifaci and Copiello [75] employed discounted cash flow analysis to examine the impact of the current tax rebate policy in Italy on stimulating private investment. Liang et al. [76] conceptualized the government and homeowners as agents and modeled their decision-making behavior using the principal-agent theory, constructing a platform for optimizing incentive policies. From the perspective of knowledge and information, formulating policies to enhance stakeholders’ understanding and awareness of improving building energy efficiency is crucial [77]. Jia et al. [78] conducted a study that highlighted the effectiveness of existing information pertaining to renovation welfare and services in improving owner cooperation. The study emphasized the importance of prioritizing professional knowledge, disclosing the sources of resources, and ensuring the completeness and the comprehensibility of building quality information.

Cluster #6, labelled “use obligation”, encompasses keywords related to “energy policy”, “sustainable energy system”, “efficiency”, “saving”, “renewable energy”, and “building environment”. This research section primarily focuses on two key aspects: renewable-energy-based heating systems, including biomass heating, heat pumps, and solar energy, as well as the obligation to use such systems. Bürger et al. [79] conducted an analysis to assess the impact of current market conditions and policy support on the further development of biomass energy in the renewable-energy-based heating market. Kranzl et al. [80] investigated the challenges of integrating renewable energy sources and rational use of energy heat policies in building a sustainable energy system, using Germany, Luxembourg, and Northern Ireland as case studies. They emphasized the high public acceptance of heat pumps due to their ability to provide enhanced comfort, suggesting that economic incentives can significantly stimulate demand for this technology. Stadler et al. [81] described the modeling approach using the Invert simulation tool and emphasized the important features required for simulating the energy system. They specifically highlighted the potential role of solar thermal systems in supplying low-temperature heat for buildings, noting that their long-term effectiveness is largely contingent on building thermal energy standards. Kranzl et al. [82] applied the simulation model Invert/EE-Lab to assess building-related heat demand in selected European countries (Austria, Lithuania, and the United Kingdom). Their findings indicated that the use obligations for renewable heating can effectively drive growth in the renewable-energy-based heating market. However, Kranzl et al. [83] pointed out that the obligation to use renewable-energy-based heating systems may result in lower adoption rates compared to subsidy programs. They highlighted the case of Austria, where widespread investment subsidies have led to a relatively high penetration of renewable-energy-based heating systems, thereby mitigating the impact of usage obligations.

Cluster #7, labelled “construction waste reduction”, encompasses keywords related to “prefabrication”, “execution”, “dynamics”, and “waste management”. This research section primarily focuses on the influence of prefabrication on reducing construction waste and managing waste afterward. Yuan [84] conducted a comprehensive analysis of the current state of construction waste management in Shenzhen, China, using a SWOT (strengths, weaknesses, opportunities, and threats) analysis. The study emphasized the importance of construction waste management and proposed various potential measures, such as waste reduction, reuse, recycling, and proper disposal, to minimize the adverse impact of construction waste. Lu and Yuan [85] evaluated the waste reduction potential of using prefabricated components in buildings based on whole-life-cycle thinking theory and demonstrated that prefabrication is a crucial strategy for effectively minimizing waste in construction projects. Tam et al. [86] conducted a study using questionnaire surveys and structured interviews to explore potential project types and procurement methods for maximizing the utilization of prefabricated building components. The results indicated that prefabrication can reduce reliance on traditional construction techniques. Aye et al. [87] investigated the potential environmental benefits of prefabrication through detailed case studies. The research revealed significant material reuse potential in prefabricated steel structure buildings, with a potential material savings of 51%, thereby contributing to a substantial reduction in construction waste. Jaillon et al. [88], through questionnaire surveys and case analyses, compared prefabrication with traditional construction methods in terms of waste reduction. The results show that, on average, prefabricated structures achieve a waste reduction level of approximately 52%. Tam et al. [89] found that prefabrication, through the use of steel formwork, can reduce wood formwork construction waste by 74% to 87% and concrete waste by 51% to 60%.

Cluster #9, labelled “sustainable construction method”, encompasses keywords related to “discount rate”, “building stock”, “carbon tax”, and “behavior economy”. This research section primarily focuses on three aspects: methods, materials, and regulations related to sustainable construction. In terms of methods, Koskela [90] introduces the concept of lean construction to minimize all types of waste in production, time, and effort, thereby maximizing the value of resources. Carvajal-Arango et al. [91] provide an overview of various sustainable methods, such as BIM, prefabrication, and quality management. Atwa [92] provided an overview of research related to the cost and trends of green buildings and further established a comprehensive model that encompasses building environmental quality, sustainability performance, and the corresponding construction processes. Alsaray et al. [93] explored sustainable construction through the development of eco-friendly concrete. At the regulatory level, Iwaro and Mwasha [94] provided a comprehensive review of building energy codes in 60 developing countries and proposed solutions to the implementation of building energy regulation.

3.4. Literature Co-Citation Analysis

Literature co-citation analysis is a valuable method used to uncover the underlying knowledge structure within a particular field [95]. Co-citation occurs when multiple publications are cited together in the literature, indicating a connection or relationship between them. A higher frequency of co-citation indicates a stronger relationship between the cited publications [96]. Additionally, the size of a node in the co-citation network reflects the frequency of co-citations, indicating the significance of a publication in the field [97]. By constructing a literature co-citation network, where each node represents a co-cited publication and the links between nodes represent the co-citation relationships, these relationships can be visualized. Figure 6 provides an overview of the literature co-citation network in this study, consisting of 127 nodes and 390 links.

To probe the significant literature in the field of BPM, the top 10 co-cited publications were identified from Figure 6. Through a comprehensive analysis of these publications, the shared knowledge foundation within the BPM field was sought to be uncovered. The extensive citation of these works underscores the significance and prominence of certain objectives within BPM research, including the mitigation of climate change, reducing energy demand, decreasing CO₂ emissions, and sustainable transitions.

Traditionally, policy mixes have been viewed as a combination of different policy instruments, without fully considering the complexity, dynamics, and potential interconnections within the actual policy landscape. Rogge and Reichardt [21] proposed an extended, interdisciplinary conceptualization of policy mixes, incorporating interacting instruments, policy strategies, processes, and characteristics. Kivimaa and Kern [98] argued that in the field of sustainable transition, the term “transition” encompasses not only the development of transformative innovations but also policies aimed at broader socio-technical system changes. Therefore, the elements of a policy mix should not only “create” new policies but also “disrupt” old ones. Smith and Raven [99] explained the concept of “protection” in sustainable transitions, analyzing three attributes of protection: shielding, nurturing, and empowerment. Studies such as that by Rosenow, Fawcett, Eyre, and Oikonomou [15] have examined the effectiveness of policy mixes by constructing a generalized framework to assess their effectiveness under specific conditions.

Furthermore, in the building sector, Webber, Gouldson, and Kerr [56] assessed household energy usage before and after the implementation of the Kirklees Warm Zone retrofitting program, aiming to explore the actual impacts of the program. Palm and Reindl [100] conducted comprehensive tracking of the entire process of multi-household retrofitting and obtained diverse understandings of the barriers to retrofitting through interviews with professionals. Charlier [101] investigated the policies of split incentives and tax credits in residential energy retrofitting.

Additionally, Shapiro [102] demonstrated that innovation policies focused solely on the innovative capacity of firms are inadequate for addressing long-term societal challenges like climate change and resource depletion. Wieczorek and Hekkert [103] integrated structural analysis and functional analysis approaches into a systematic policy framework, identifying systemic issues and proposing systemic tools for addressing these issues in innovation systems research. Weber and Rohracher [104] introduced a comprehensive framework that combines market failures, structural system failures, and transformation system failures, providing support for innovative policies in the context of long-term transformations.

3.5. Evolutionary Trend Analysis

The research trend of BPM can be visualized using a time zone diagram, as depicted in Figure 7. In this diagram, each keyword is positioned based on the year it first appeared, while the connections between keywords represent their inherent relationships [24]. Furthermore,

Table 3. Top 19 keywords with the strongest citation bursts.

Keywords	Strength	Begin	End	2004–2023
China	1.19	2012	2015	▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂▂▂▂▂
Building energy efficiency	0.65	2012	2019	▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▂▂▂▂
Policy mix	1.43	2016	2019	▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂
UK	1.23	2016	2019	▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂
Climate policy	1.23	2016	2019	▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂
Policy package	0.98	2016	2019	▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂
Impact	1.42	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Governance	1.4	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Performance	1.03	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Framework	1.03	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Country	0.94	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Evolutionary game	0.79	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Energy	0.79	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Energy efficiency policy	0.71	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Consumption	0.71	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Retrofit	0.68	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Split incentive	0.68	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Environmental policy	0.68	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃
Energy transition	0.68	2020	2023	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃

presents the detection of keyword bursts in the BPM field from 2004 to 2023, featuring a total of 19 burst keywords sorted chronologically according to the year they experienced a burst. Each red line in Table 3 indicates the duration of each corresponding keyword.

Based on Figure 7, the research on BPM has become increasingly widespread and can be divided into two stages. The blue and green sections represent the first stage, which corresponds to the initial exploration of BPM research. During this stage, the concept of policy mix was relatively vague, with a greater focus on implementing individual policies, allocating responsibilities among various functional departments, and promoting sustainable development within the building sector. This encompassed areas such as the renewable energy market and construction waste management. For example, in Sweden, one of the main characteristics of environmental policy mixes is the departmental responsibility system, where the National Board of Housing, Building, and Planning is responsible for the management of the construction and real estate sectors as part of its duties [105,106]. In countries like Lithuania and Austria, the utilization of renewable energy for heating purposes has reached a relatively high level of development [107]. Moreover, research conducted in this field often employs modeling methods, such as system dynamics, to simulate factors like energy consumption in buildings. For example, Li and Li [108] established a system dynamics model to simulate the impact of promotional policies on the behavior of participants in adopting new technologies in the construction industry. They also investigated the effects of various combinations of promotional policies. Similarly, Kranzl et al. [109], utilizing the Invert simulation tool, calculated the potential reduction in carbon dioxide emissions and the related public expenditure for different policy mixes.

The yellow and red sections represent the second stage, which involves researching specific policy tools such as financial incentives and regulations, analyzing the potential impacts of policy mixes, and identifying existing barriers. These barriers are related to various aspects, including policy formulation and implementation processes, goal consistency, and building energy efficiency. For example, in the UK and Turkey, commonly employed policy toolsets include regulatory schemes, market-based/financial schemes, and informational measures [110]. In Finland, the commonly utilized toolset consists of economic tools, regulatory tools, and various flexible measures [111]. Furthermore, a study conducted in South Korea highlighted the necessity of effective policy coordination among government departments when formulating credible long-term policy objectives [45]. The emergence of keywords such as renewable energy, energy efficiency, climate change, and energy transition, as well as carbon price and carbon tax, indicates a comprehensive and specialized survey of the field. This shift moves away from a focus on a single building or energy sector and encompasses a broader range of sectors, along with more comprehensive concepts.

Burst words, defined as keywords that experience a sudden and explosive increase in frequency within a short period of time [112], have garnered significant attention from the scientific community in a relatively brief timeframe [113], making them a focal point of current research. As indicated in Table 3, there has been a substantial surge in the usage of terms such as “policy mix”, “climate policy”, and “policy package” since 2016. Notably, the terms “policy mix” and “climate policy” were employed in the studies conducted by Edmondson, Rogge, and Kern [13] and Nascimento et al. [114], respectively. Similarly, Segal, Feitelson, Goulden, Razin, Rein-Sapir, Kagan, and Negev [57] employed the term “policy package” and acknowledged the absence of a universally applicable policy package. These terms have witnessed increased prevalence and attained a stable state post 2019, indicating a consistent usage pattern.

Likewise, the term “building energy efficiency” has exhibited significant growth since 2012 and has become widely adopted after 2019. Scholars have conducted insightful studies on building energy efficiency from diverse perspectives, such as policy [46] and behavioral decision-making [115].

Based on the findings presented in Table 3, a comprehensive review of the contextual meaning of the keywords in the literature was conducted, ultimately leading to the categorization of research frontiers into several key areas, such as politics (governance, performance), energy (energy, energy transition), policy (energy efficiency policy, environmental policy, impact, and framework), policy instruments (retrofit, split incentive), and consumption and evolutionary gaming.

4. A Roadmap for BPM

Based on the findings of the BPM analysis, this study presents a comprehensive knowledge roadmap (Figure 8). The roadmap integrates the underlying connections between knowledge hotspots, methodology, frontiers, and domains, providing a holistic understanding of the BPM field. The research hotspots/frontiers section is the result of combining keywords co-occurrence and burst keywords to summarize six important themes while avoiding repetitiveness. The knowledge domains consist of nine main sections, each with a theme, and the keywords under each theme are also shown in Figure 8. These keywords constitute important research elements within the different research domains. In addition, the methodology contains both specific research methods and key theories.

• Research hotpots and frontiers

The keywords co-occurrence analysis and evolutionary trend analysis identified research hotspots and frontiers in the field of BPM. This section integrates the aforementioned research findings, considering their intersection. In the policy domain, specific topics of interest revolve around various aspects, such as building energy efficiency policy [50], split incentive [53], carbon tax [67], and carbon pricing [66]. These areas investigate the combination and effectiveness of policy instruments and strategies to address building sustainability. Within the energy field, the key subjects encompass energy consumption and energy transition. Research in this area, for instance, focuses on reducing consumption [72], adopting renewable energy sources [79], and addressing the challenges associated with transitioning to a greener energy system [91]. The realm of politics involves examining the governance and management of government departments. Researchers assess sectoral coordination [51], evaluate differences in governance goals and styles across policy areas [116], and conduct in-depth analysis of the impact of governance structures on environmental and energy-related issues [117]. In the building sector, the research emphasizes green building practices and retrofitting existing buildings. This includes exploring energy-efficient construction methods [90], sustainable materials [93], and technologies [86] to improve the energy performance of buildings. The innovation system and evolutionary game are additional areas of focus in research. These topics delve into the dynamics of innovation processes [98] and the dynamic evolutionary game of policy configuration under different scenarios [82].

• Deepened insight into interdisciplinary policy mixes

The evidence from research domains, hot topics, and trends indicates that BPM research encompasses a broad range of interdisciplinary themes, including energy, engineering technology, politics, policy, and innovation, among others. These themes transcend the boundaries of any single academic discipline. Given the complexity of the construction industry, which involves multiple stages such as investment, design, construction, and operation, collaborative efforts across various disciplines are inherently necessary.

However, the challenges identified in policy implementation contribute to the complexity of interdisciplinary policy integration in the building sector. Research conducted in Austria has identified several obstacles that hinder the implementation of different policies, including decentralized jurisdiction, lack of sectoral integration, inconsistent goals, and insufficient targeting [117]. Furthermore, disparities between local and national levels have been highlighted by Gram-Hanssen, Jensen, and Friis [54] in their study on local governance strategies for homeowner participation in energy efficiency retrofit across 12 Danish cities. While local authorities have taken commendable measures to involve homeowners, the national policy mix falls short in providing comprehensive support. This emphasizes the central challenge of mismatched local, national, and even international climate policies in building energy efficiency retrofitting. Nykamp [118] argues that conflicts and inconsistencies are inevitable due to differences in governance objectives and styles across various policy domains.

Addressing the complex issues within the building sector necessitates a comprehensive approach that takes into account policy strategies, features, and processes. To tackle these challenges, policymakers can adopt an expanded concept of policy mix, as proposed by Rogge and Reichardt [21]. This concept incorporates a broader range of policy instruments and approaches, providing policymakers with more options to address the complexities of the building sector. By diversifying their policy toolkit, policymakers can tailor interventions to specific challenges and leverage synergies between different policy measures. Furthermore, policymakers can benefit from incorporating a “creative destruction engine” approach, as advocated by Kivimaa and Kern [98]. This expanded perspective surpasses the traditional technology-push and demand-pull instruments, allowing for the inclusion of a broader array of policy instruments in a coherent mix tailored for facilitating a sustainability transition. In addition, the coordination, feedback, and evaluation processes in policy formulation and implementation are of utmost importance. These processes ensure effective policy implementation, enable adjustments based on feedback, and provide opportunities for continuous evaluation and improvement.

• Methodology

Previous studies have employed a diverse range of methods and theories to gain insights into the field of BPM. For instance, Urge-Vorsatz et al. [119] conducted a comprehensive analysis of over 60 ex post policy evaluation reports from 30 countries and country groups. Their study aimed to assess the effectiveness of policy instruments such as appliance standards, building codes, and tax-exempt voluntary labeling in promoting energy efficiency. Ma et al. [120] employed a fuzzy set qualitative comparative analysis approach to explore the configuration of policy instruments and assess their impact on low-carbon city development. This approach aimed to bridge the gap between theoretical knowledge and the practical implementation of policy instruments in the context of developing low-carbon cities. Additionally, Rosenow, Fawcett, Eyre, and Oikonomou [15] reviewed the current policy mixes in 14 EU countries and assessed the interactions between these policies. Toller et al. [121] proposed a novel assessment method based on the life cycle of input–output analysis, enabling the regular monitoring and prioritization of different improvement measures. Casado-Asensio and Steurer [122] adopted a case study approach to investigate the integration of climate change issues into building policy, revealing the adverse effects of decentralization on climate change mitigation efforts.

Despite variations in publication time, research questions, and geographical distribution, these studies have made significant contributions to the field of BPM. Through a review of the methodology utilized in 67 literature sources, we have identified and compiled the main research methods and theories utilized in the BPM field (see Figure 8). While these methods and theories may differ in their applicable conditions, their identification serves as a valuable reference for future BPM research.

• Research prospects

Although extensive research has been conducted on BPM, the complexity of the field still necessitates further investigation. One significant research prospect involves the development of a comprehensive framework for evaluating the effectiveness of specific policy combinations under diverse contextual conditions. By adopting a more comprehensive approach, researchers and practitioners can gain a deeper understanding of how different policies interact and influence outcomes within specific contexts. This will enable them to identify the most effective policy combinations and recognize the contextual dependencies that affect their effectiveness. By bridging the gap between isolated policy measures and considering their combined effects, this research prospect holds great potential for advancing the field of BPM and enhancing policy decision-making processes.

Another promising research avenue involves capturing the intricate nature of actual policy mixes and understanding their underlying political dynamics. It has identified that politics is a major research branch of BPM. By focusing on political dynamics, researchers can gain valuable insights into how policy mixes are formulated, evolve over time, and ultimately produce desired outcomes. Understanding the political dynamics behind policy mixes is crucial for designing policies that are not only effective but also adaptable to changing circumstances. By considering the interplay between political factors and policy outcomes, researchers can contribute to the development of more nuanced and contextually appropriate policy mixes.

Addressing the incoherence among different policies in terms of their objectives presents another research prospect. Coordinating and aligning policy objectives across multiple sectors, regions, and levels can significantly enhance the overall effectiveness of a policy mix. Future research can focus on identifying the root causes of conflicts that arise among different policy types, exploring methods for effectively coordinating policy objectives, and devising strategies to mitigate conflicts.

Efforts can be directed towards identifying solutions and best practices that address the specific challenges faced in implementing building energy efficiency policies. This may involve exploring innovative approaches for code adoption, such as providing incentives or streamlining the regulatory process. Additionally, evaluating and enhancing enforcement mechanisms can help overcome obstacles that limit compliance and enforcement effectiveness.

5. Conclusions

Efforts to enhance sustainable development and reduce carbon emissions in the building sector heavily rely on effective policy mixes. Various initiatives, regulations, and strategies have been implemented worldwide to promote sustainable practices in construction. However, the inherent complexity of the building sector, involving multiple phases of work and numerous stakeholders, presents unique challenges. Single-policy instruments often prove insufficient in addressing these challenges in a timely and effective manner. Consequently, researchers have recognized the need for comprehensive approaches in the form of policy mixes to tackle the complexities of the sector. Despite multiple explorations in this area, fragmented studies have hindered our comprehensive understanding of BPM, resulting in isolated findings and limited insights into the broader context of BPM.

In this study, we utilized the scientometrics method with the assistance of the Cite Space 5.7 R5 to uncover the knowledge landscape in the field of BPM. We reviewed a total of 67 BPM-related literature sources and recognized over a hundred significant keywords. Through clustering analysis, nine crucial research domains were identified. Co-citation analysis and evolutionary trend analysis were employed to explore the underlying knowledge structure and research dynamics in BPM. Based on these analyses, a knowledge map was developed, and potential future research directions were proposed. These findings also have policy implications for promoting sustainable development in the building sector, which involve adopting a comprehensive understanding of policy tools and their interactions, leveraging policy characteristics to foster synergies, considering the political dynamics, and aligning policy objectives across different sectors, regions, and levels, as well as systematizing the formulation, implementation, and evaluation of building policies.

This study contributes to a better understanding of the research landscape in BPM and provides valuable guidance for policymakers, researchers, and industry professionals seeking to advance sustainable practices in the building sector. By identifying key research domains and frontiers, our study offers insights into the current state of BPM research and highlights areas that require further exploration. These findings can inform the development of comprehensive and effective policy mixes that address the complexities of the building sector, ultimately leading to more sustainable and energy-efficient buildings. It is worth noting that the findings of this study are based on the current state of the BPM research field, and the applicability of these results may change over time with the evolution of sustainable development challenges. Therefore, it is encouraged that future research maintains continuous attention and exploration in this field in order to track new insights and developments, and to adjust research findings to adapt to the ever-changing context.

There are some limitations in this study. First, through a rigorous and careful process of collection and screening, a total of 67 sample documents were obtained. The majority of these samples were sourced from countries and regions such as China, the Netherlands, the United Kingdom, Germany, Austria, and Australia. However, it is important to acknowledge the inherent disparities in development levels, technological advancements, and cultural diversity across different regions worldwide. Therefore, it is crucial to note that the findings derived from these samples may not be universally applicable. When applying the findings of this study in practical contexts, it is essential to conduct specific situational analysis, taking into account the unique characteristics and contextual factors of each region. As the body of relevant research expands, future studies can also aim to incorporate representative samples that account for regional development. Second, drawing on existing research [26,43], the literature used in this study primarily consists of journal papers. Although they provide a robust literature foundation for constructing the BPM knowledge framework, the absence of institutional documents (national or international) as samples may limit the breadth of our analysis. To address this limitation, future research endeavors can incorporate institutional documents, allowing for a more comprehensive exploration of BPM. Third, in the knowledge roadmap section, we emphasized the criticality of interdisciplinary research in the BPM field and explored its implications. However, considering the complexity and systemic nature of interdisciplinary studies, these discussions remain limited. Future research can further deepen the examination of interdisciplinary aspects in BPM.